The radio-frequency quadrupole linear accelerator design was first conceived in the 1970's and was initially presented as the ‘missing link’ towards high power beams. The early designs of RFQs allowed an efficient preparation of high-intensity, low-energy hadron beams for acceleration in a drift tube linac (DTL), thereby boosting the efficiency of transfer between a source and a DTL accelerator from 50% to more than 90%.
Typical RFQ accelerators are configured to focus, bunch and accelerate a continuous beam of charged particles with high efficiency, while preserving the emittance. The bunching of the RFQ is typically performed adiabatically over several cells so as to ensure maximum beam capture. Existing RFQ designs aim to maximise capture and thereby minimise beam losses, as beam losses are traditionally associated with risks such as the activation of the surrounding environment.
An example of an existing RFQ design is the CERN Linac4 RFQ, which is designed to reach energies as high as 3 MeV, and requires a length of 3 meters to achieve this output energy. In certain applications like injection into hadron therapy linacs for cancer treatment, much higher energies are required, such as 5 MeV or 10 MeV or even higher. However, higher energies typically require much longer, RFQs; and this can make it impractical to use the RFQs in environments such as hospitals. For example, the IPHI RFQ can reach a 5 MeV energy output, but at over 6 meters in length, this may be too large to be practical.
There is therefore a need for compact RFQ designs that are capable of producing high energy particle beams.